The subunit structure of the enzyme deficient in Tay-Sachs and Sandhoff's diseases has been more carefully defined than in any other autosomal recessive defects. Using homogeneous preparation of hexosaminidase A derived from human placenta and kidney it has been possible to dissociate the enzyme into three fractions designated as alpha, alpha 8, and 'beta' polypeptides. the beta polypeptides reassociated to form enzymatically active protein similar to hexosaminidase B. The alpha 2 and alpha 8 polypeptides were found to be enzymatically inactive and cross-reacted with anti-hexosaminidase A but not with anti-hexosaminidase B antisera. These studies further supported our hypothesis that hexosaminidase A is (alpha beta)3 and hexosaminidase B is (beta beta)3. The antibodies raised against glutaraldehyde cross-linked alpha 2 and alpha 8 fractions were found to be monospecific to hexosaminidase A and did not cross-react with hexosaminidase B. Using these antibodies, it was possible to demonstrate the presence of cross-reacting material in eight unrelated cases of Tay-Sachs disease. Attempts are now being made to quantitate and purify the cross-reacting material in Tay-Sachs disease by using radioimmunoassay. The defective protein in Tay-Sachs disease will be characterized by amino acid analysis, subunit structure, molecular weight determination and amino acid sequencing. The quantitation of cross-reacting material in Tay-Sachs disease would further improve the heterozygote determination and offer a means of prenatal diagnosis of Tay-Sachs variants. Enzyme replacement therapy using liposomes as a vehicle for delivering hexosaminidase A will be tried on experimental animals. The distribution of hexosaminidase A labeled with 125 I will be followed in mice after intraperitoneal and intraveneous injections and the toxicity studies will be performed. BIBLIOGRAPHIC REFERENCES: Cohen, Charles, M., Gerald Weissmann, Sylvia Hoffstein, Yogesh C. Awasthi, and Satish K. Srivastava. 1976. Introduction of purified hexosaminidase A into Tay-Sachs leukocytes by means of immunoglobin-coated liposomes. Biochem. 15: 452-460. Wiktorowicz, J.E., Y.C. Awasthi, and S.K. Srivastava. 1976. Confirmation of the unique and common subunit theory to explain interrelationship of hexosaminidase A and B.